Laravel model issue (non-object) - php

Question

I am using Laravel 5.3 and this model:
namespace App\Models;
use Illuminate\Database\Eloquent\SoftDeletes;
use Illuminate\Support\Facades\Storage;
use Illuminate\Database\Eloquent\Model;
class Category extends Model
{
use SoftDeletes;
protected $table = 'categories';
protected $fillable = [
'name',
'slug',
'description',
'thumbnail',
'parent',
'created_by'
];
protected $hidden = [
'created_by'
];
protected $dates = ['deleted_at'];
public static function getSubcategories($category)
{
return Category::whereParent(Category::whereSlug($category)->first()->id)->get();
}
}
It works perfectly on my localhost server, but when I upload it on my production server, it outputs following error:
Trying to get property of non-object (on line ....)
It is on this line:
return Category::whereParent(Category::whereSlug($category)->first()->id)->get();
(Lines are hidden, because this model has much more functions and would be too long for this post)
Full trace:

Answer 1

its because the Category::whereSlug($category)->first() is returning null and that you are trying to get id of that null. so its as the error states that you are trying to get a property of non object.
I see that you are trying to get self reference category. you could so it this way as a relationships.
//children
public function categories()
{
return $this->hasMany(self::class, 'parent');
}
//parent
public function parent()
{
return $this->belongsTo(self::class, 'parent');
}
if you want to select recursively you could add this too.
public function parentRecursive()
{
return $this->parent()->with('parentRecursive');
}
public function categoriesRecursive()
{
return $this->categories()->with('categoriesRecursive');
}